Flight Instructor and Student Pilot experiences a near miss with a UFO. Approximately 50 ft. from wing.

My student and I were performing a long cross country IFR flight. We departed our home airport, French Valley, to Santa Barbara airport.
The type of aircraft we were flying is a Piper Archer.
Estimated time of event was 16:15 Pacific time.
Indicated altitude was approximately 6,100 ft MSL (Mean Sea Level).
Indicated Airspeed was 105 KTS.
Approximate position was over Van Nuys Airport/ Burbank Airport, 2 – 5 miles West of VNY VOR, on the V186.
Heading 280 degrees, North West bound.
 Preceding the event, I remember ATC (Air Traffic Control) informing us of various aircraft around our present position. I was looking down at my iPad to look for any incoming traffic to maintain separation. As I looked at our position on the screen, there were multiple targets around our position that did not seem to be a factor as they were pretty far from our location.
 The alarming and confusing matter was that the Garmin 430’s TCAS (Traffic Collision Avoidance System) was going off giving me a collision alert. It was depicting a target -100 ft from our position at our 12 o’clock, and it was moving fast towards us, opposite direction. I began to panic as this is very close.
 My student pilot in the left seat yelled, “Oh My God”, and jerked the aircraft controls.
From my point of view, I was sitting in the right seat, as I looked outside to search for this fast aircraft 100 ft below us I saw a dark gray metallic figure dip low and pass right underneath our left wing. It looked like it made that it made a last-minute maneuver to avoid us. visually it seemed closer to being within 50 ft. I was able to quickly glance at the object as it was to my left.
 This UFO looked closely like an oval, teardrop, or a tight dish-like shape, and very aerodynamic like. To me it looked like a mix between a fossilized trilobite with a smooth carapace, or flying manta-ray/turtle. The size of the object was approximately the size of a small jet like a Honda Jet or a very wide sports car. From my memory the top side of the object appeared to be made of metal as I saw metal plates that resembled closely to the top side of B2 bomber or a F-35 aircraft. I knew it was metal as I was able to see the sun reflecting it’s shine from the top of the object into my eyes. This event lasted less than 2 seconds and happened quickly. The object maneuvered incredibly fast.
 After the event, my student was terrified as she was asking me what had almost collided with our plane. I gave her my description of what I saw and she confirmed and said it looked more like a flying saucer. She was able have a closer look as she was closer to the object and had a better view of it.
 I look back down to my iPad to verify if it was still close by and the G430 and it was gone.
 My thoughts: The weird thing is that if this was a UFO made by a sophisticated intelligent life form outside of our known planet, it should not have a transponder or a signal that our technology should pick up. The other contradictory factor is that why would a military aircraft operate in close vicinity of congested airspace. The other factor is that a flying object like that with our present technology shouldn’t be capable of cruising at those high speeds. Even fast-moving large aircraft, such as B747, would appear to be moving slowly from the ground or in air.
 Did we feel the wake turbulence? No because we were above the UFO, and wing tip vortices sink towards the ground. It couldn’t have been a bird either or balloon either as the size was just far too large to match the profile of what we experience.
 We did not report our experience to ATC as we were very shocked from the event.
 Looking back at my track logs of Foreflight, there appears to be a good 3 minutes of my flight data missing during the approximate time of the event.
((NUFOC Note:  We spoke at length via telephone with this witness, and we found him to be serious-minded.  We suspect he is an excellent witness, and highly reliable.  We are expecting to receive a supplementary report from the student pilot, as well.  PD))